Strange Tonearm Tweak. Long

Stefano, I don't have any photos. But I can explain.

First, we must look at the way that I have the hanging counterweight slung under the tonearm. I use a length of Spectra fishing line, which is high-tensile non-stretch line. Then I hang the long shaft-shaped counterweight on 2 points(each end of the weight) and sling the line over the tonearm. This gives the mass effect in the lateral plane as well as horizontal.

Then we must look at what we are trying to accomplish. First, it is understood that the counterweight mass should be as near the plane of the record as possible, for best tracking ability. The standard Rega counterweight does nothing in this regard, as the mass is all centered at the same plane as the tonearm. The Expressimo Heavyweight does lower the plane of the mass(by making the hole off-set) and has more of the mass below the tonearm, for better tracking. But the off-set hole causes the tonearm to shift tracking force when the arm rides up over a warp, because the mass distribution is unequal in the vertical plane, and when the arm rides up over a warp, the bulk of the mass of the Heavyweight actually moves foward around its rotational circle(which is different than the rotational circle of the tonearm). Additionally, the mass that is below the tonearm on the heavyweight only comprises a relatively small shift in the center of gravity of the counterweight mass(although it is audible improvement). It has a price, and that is the counterweight mass is no longer symmetrical when the arm is in vertical motion. This is the reason why Mark Baker is not using an off-set counterweight on his OL tonearms.

Now, to make the full step to making ALL the mass of the counterweight at the same plane as the record, for best results, requires some different implementations. First, the mass must be equally distributed in all planes for symmetrical operation during movement of the tonearm during play. Second, it must provide the normal counterweight functions, which are balancing the arm, providing tracking force, and providing a certain amount of lateral stabilization.

By hanging a shaft-shaped counterweight cross-wise under the arm end-stub, we can hang it like a child's playground swing, with the string slung over the end stub. By slinging the string over the end-stub, we have lateral stabilization as well as vertical, because the string wraps over the end-stub and has enough contact around the diameter to provide the mass effect laterally on the tonearm. The non-stretch string(Spectra fishing line) provides a solid tie to the counterweight on each end, thus effectively making the counterweight operate as a solid tie to the tonearm in the lateral and horizontal planes. However, the counterweight will still "yaw" in the "z plane"(fore and aft), so that the counterweight mass will remain plumb under the end-stub of the tonearm during rise and fall during warp play, and still retain the correct tracking force, and still maintain the correct position of center of gravity down near the plane of the record.

The result is that ALL the mass of the counterweight is now moved to the correct position at the same level as the record, not just some of it. Also, the mass remains efffectively constant during vertical movement of the arm. Third, and possibly most important, the mass is effectively mechanically decoupled from the end-stub, which results in a free-er sound, less encumbered by high mass and addtional parts, so its natural resonant properties may occur with less reflection and harmonic effects due to 2 different masses being coupled together by a screw at a random point on the end-stub. The string has a natural resonance damping effect by simply vibrating, and the ends of the string are placed into the lead mass of the counterweight shaft, which has sufficient mass to absorb and damp the vibrations.

Regarding your question about horizontal stabilization effects, the hanging counterweight is coupled horizontally well enough to provide this stabilization function. Remember, that the purpose of horizontal stabilization in the tonearm is to prevent it from being moved by the compliance of the cartridge during play. If it gets into motion from these forces, we have already failed to stabilize it. It is the "static moment of inertia" which we are dealing with here. The amount of force needed to start this body into motion. If the static moment is higher than the cartridge(on the arm) can apply, then the arm will be stable, and not be moved into unwanted motion by the forces applied by the cartridge, and the performance will increase, because all the stylus movements will then be generated into electrical signal, and not lost in unwanted arm movement.

I wish to mention however, that this is a small increase in performance, not on the level of the HiFi mod. It will add to the sonic performance of the arm in an amount of a few percent. The liquidity is better, and the sound is more open.

I have found that just slinging the string over the arm, results in a "crawling" effect of the string on the end-stub. This causes change in tracking force, and is unacceptable. I then put a rubber O-ring on the end stub, to act as a "stop" for the string, so that the string cannot crawl toward the back of the end-stub, which is where it wants to go. It is not needed to put an O-ring in front of the string, because the string only wants to crawl backward. It also acts as a guide for replacement of the counterweight, if you ever want to remove it for cleaning or anything. You just put the string back on the end-stub, just contacting the front of the O-ring, and you have your pre-set tracking force established. Setting the tracking force with the O-ring is place the first time, is a bit finicky, and can be tedious. But once it is placed, the position is set, until you move the O-ring. If you want to make small VTF adjustments, it is advisable to use Doug's VTF on the fly modification, since small VTF changes with the O-ring is a pain in the ass.

I've used the C/W Twl just described on my O/L Silver, based on his description earlier on this thead. I can confirm all the sonic changes and benefits he described. One more tip: adjust the mass of the weight so you can hang the thing as close to the pivot as practical for proper cartridge balancing and VTF. This should improve warp tracking and reduce the weight's tendency to swing.

I would not necessarily want to use a free hanging C/W on a floaty, suspended TT. On a solid, nonsuspended one it's a nice upgrade. Not as big as the HIFI Mod, like Twl said, but it really does reduce armtube resonance reflections. This results in less overhang on virtually all notes, for a cleaner and tighter presentation. Recommended if you can deal with a bit of fiddliness. The O-ring is essential, the C/W would be insufferable without it.

For anyone wondering, I just deleted the post I made here yesterday. I'm working on replacing it with something I hope is a little more sensibly thought-out...

Yes, Alex, I was wondering about that. Looking forward to your re-post.

OK Tom, without going into every detail to the Nth degree, here's what's on my mind now:

First of all, I'm not sure I fully understand why or if it's necessarily desirable to decouple the counterweight. Or to go for lowest mass in general.

But if we assume that these are desirable goals, then why not get completely rid of the coupled mass of the counterweight? Hanging the weight off the end of the tonearm's rear extension seems like it would invite a swinging motion in response to energy inputs at the stylus, since the string can't perfectly decouple the weight. Additionally, the weight would be free to oscillate in response to spurious energy inputs to the plith as a whole, such as from loud bass notes or footfalls.

Today's post is a simpler design then in the post I deleted. End the tonearm at the pivot point, with no extension continuing behind it. Take a cue from the design of a conventional suspended-weight anti-skating arrangement. Hang a weight from a string, run it over a hanger positioned above the tonearm, and attach the string to the tonearm (moveable to fine-adjust VTF). The force of gravity pulling down on the weight now pulls up on the tonearm, offsetting the force of gravity pulling down on the tonearm/cartridge, minus the desired tracking force.

The hanger is mounted on the horizontal bearing housing, in order that there will be no lateral relative motion between the hanger and the tonearm. The hanger (and therefore the weight as well) must rotate along with the tonearm in the lateral plane so that it ignores the lateral component of the tonearm's movements. With the directly-hung counterweight described above, motions of the tonearm in both planes affect the motion of the counterweight. The counterweight 'sees' all the vectors and reacts accordingly. But with an intermediate hanger to run the string over, like is used for anti-skate, motions of the tonearm in both planes have only their vertical component transmitted to the counterweight. The counterweight 'sees' only vertical inputs, and accordingly moves strictly up and down, rather than like a pendulum.

But the counterweight might still move in response to spurious inputs. So, give it a streamlined shape and immerse it a dampening fluid bath. The trough, like the hanger and the weight, will have to ride on the horizontal bearing housing. But this might not be a bad thing, since we removed the mass of the tonearm's rear extension and attached counterweight, and we might want to bump up the tonearm's lateral mass in isolation, like you do with the HiFi mod.

Anyway, if decoupling the counterweight is what we want, then I can't think of many ways to decouple it further than this. I'm just not sure it would accomplish anything...